Nanofluidics of Single-Crystal Diamond Nanomechanical Resonators
Letter pubs.acs.org/NanoLett
Nanofluidics of Single-Crystal Diamond Nanomechanical Resonators V. Kara,† Y.-I. Sohn,‡ H. Atikian,‡ V. Yakhot,† M. Lončar,‡ and K. L. Ekinci*,† †
Department of Mechanical Engineering, Division of Materials Science and Engineering, and the Photonics Center, Boston University, Boston, Massachusetts 02215, United States ‡ Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States ABSTRACT: Single-crystal diamond nanomechanical resonators are being developed for countless applications. A number of these applications require that the resonator be operated in a fluid, that is, a gas or a liquid. Here, we investigate the fluid dynamics of single-crystal diamond nanomechanical resonators in the form of nanocantilevers. First, we measure the pressuredependent dissipation of diamond nanocantilevers with different linear dimensions and frequencies in three gases, He, N2, and Ar. We observe that a subtle interplay between the length scale and the frequency governs the scaling of the fluidic dissipation. Second, we obtain a comparison of the surface accommodation of different gases on the diamond surface by analyzing the dissipation in the molecular flow regime. Finally, we measure the thermal fluctuations of the nanocantilevers in water and compare the observed dissipation and frequency shifts with theoretical predictions. These findings set the stage for developing diamond nanomechanical resonators operable in fluids. KEYWORDS: NEMS, nanomechanics, nanofluidics, diamond, surface accommodation
S
In this article, we present a systematic study of the oscillatory nanofluidics of single-crystal diamond nanomechanical resonators. We explore a broad parameter space, focusing on both the resonator length scale (size) and the resonance frequency. Previous works typically focused on only one of these parameters, that is, either the frequency14−17 or the length scale.18 We show conclusively how a subtle interplay between the length scale and the frequency determines the nature of the flow induced by nanomechanical resonators resulting in lowfrequency and high-frequency regimes. We also compare the surface accommodation coefficient of heavy (N2, Ar) and light (He) gases on diamond resonators and determine that diamond surface accommodates these gases differently. Finally, we measure the thermal fluctuations of the nanomechanical resonators in water and compare these measurements with theory.19−21 Figure 1a shows scanning electron microscopy (SEM) images of a set of diamond nanomechanical resonators. To make these devices, we use a method similar to the angledetching fabrication technique described earlier.22 This technique was developed due to a lack of a mature thin-film technology for depositing single-crystal diamond. Briefly, we first perform a standard vertical etch using oxygen plasma, with a second etch step done at an oblique angle. Figure 1b shows the sidewalls of one of the cantilevers; the inset is a crosssectional image. To take these images, the diamond nanocantilevers are transferred onto an evaporated silver film by flipping
ingle-crystal diamond has unique and attractive mechanical properties, such as a high Young’s modulus, a high thermal conductivity, and a low intrinsic dissipation. Recent advances in growth and nanofabrication techniques have allowed for the fabrication and operation of nanometer scale mechanical systems made out of single-crystal diamond. Part of the research community in diamond nanomechanics is focused on coupling the negatively charged nitrogen vacancy (NV−) with a mechanical degree of freedom.1−4 There are significant efforts for realizing diamond nano-opto-mechanical systems5−7 for quantum information processing and optomechanics. Diamond nanocantilevers are also being developed for ultrasensitive magnetometry8,9 and scanning probe microscopy (SPM).10 In addition, it has been suggested that the chemistry of the diamond surface may be amenable to surface functionalization11 for sensing. To date, the performance of single-crystal diamond nanomechanical resonators has been thoroughly evaluated in vacuum.1,6,7,12 However, vacuum properties will be of little relevance for some applications, such as mass sensing, magnetometry and SPM. Instead, performance in fluids will be consequential especially, when biological or chemical samples are being analyzed in ambient air or in liquids. It is therefore important to elucidate the nanoscale fluid dynamics (or nanofluidics) of diamond nanomechanical resonators. The smooth and inert surface of single-crystal diamond may provide unique opportunities for high-performance operation in fluids. For instance, gases may be accommodated favorably on the diamond surface; the inherent inertness of the diamond surface may allow for reduced drag in water.13 © 2015 American Chemical Society
Received: August 31, 2015 Revised: October 22, 2015 Published: October 28, 2015 8070
DOI: 10.1021/acs.nanolett.5b03503 Nano Lett. 2015, 15, 8070−8076
Letter
Nano Letters
Returning to Figure 1a, we identify several interesting features. Because of angled-etching, the cross sections of the cantilevers are not rectangular but triangular. Figure 1b shows that most of the sidewall surfaces are smooth with an estimated root-mean square (rms) roughness ≲10 nm. The top surface of the cantilever is protected during etches and is much smoother, with an rms roughness
Nanofluidics of Single-Crystal Diamond Nanomechanical Resonators V. Kara,† Y.-I. Sohn,‡ H. Atikian,‡ V. Yakhot,† M. Lončar,‡ and K. L. Ekinci*,† †
Department of Mechanical Engineering, Division of Materials Science and Engineering, and the Photonics Center, Boston University, Boston, Massachusetts 02215, United States ‡ Harvard John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United States ABSTRACT: Single-crystal diamond nanomechanical resonators are being developed for countless applications. A number of these applications require that the resonator be operated in a fluid, that is, a gas or a liquid. Here, we investigate the fluid dynamics of single-crystal diamond nanomechanical resonators in the form of nanocantilevers. First, we measure the pressuredependent dissipation of diamond nanocantilevers with different linear dimensions and frequencies in three gases, He, N2, and Ar. We observe that a subtle interplay between the length scale and the frequency governs the scaling of the fluidic dissipation. Second, we obtain a comparison of the surface accommodation of different gases on the diamond surface by analyzing the dissipation in the molecular flow regime. Finally, we measure the thermal fluctuations of the nanocantilevers in water and compare the observed dissipation and frequency shifts with theoretical predictions. These findings set the stage for developing diamond nanomechanical resonators operable in fluids. KEYWORDS: NEMS, nanomechanics, nanofluidics, diamond, surface accommodation
S
In this article, we present a systematic study of the oscillatory nanofluidics of single-crystal diamond nanomechanical resonators. We explore a broad parameter space, focusing on both the resonator length scale (size) and the resonance frequency. Previous works typically focused on only one of these parameters, that is, either the frequency14−17 or the length scale.18 We show conclusively how a subtle interplay between the length scale and the frequency determines the nature of the flow induced by nanomechanical resonators resulting in lowfrequency and high-frequency regimes. We also compare the surface accommodation coefficient of heavy (N2, Ar) and light (He) gases on diamond resonators and determine that diamond surface accommodates these gases differently. Finally, we measure the thermal fluctuations of the nanomechanical resonators in water and compare these measurements with theory.19−21 Figure 1a shows scanning electron microscopy (SEM) images of a set of diamond nanomechanical resonators. To make these devices, we use a method similar to the angledetching fabrication technique described earlier.22 This technique was developed due to a lack of a mature thin-film technology for depositing single-crystal diamond. Briefly, we first perform a standard vertical etch using oxygen plasma, with a second etch step done at an oblique angle. Figure 1b shows the sidewalls of one of the cantilevers; the inset is a crosssectional image. To take these images, the diamond nanocantilevers are transferred onto an evaporated silver film by flipping
ingle-crystal diamond has unique and attractive mechanical properties, such as a high Young’s modulus, a high thermal conductivity, and a low intrinsic dissipation. Recent advances in growth and nanofabrication techniques have allowed for the fabrication and operation of nanometer scale mechanical systems made out of single-crystal diamond. Part of the research community in diamond nanomechanics is focused on coupling the negatively charged nitrogen vacancy (NV−) with a mechanical degree of freedom.1−4 There are significant efforts for realizing diamond nano-opto-mechanical systems5−7 for quantum information processing and optomechanics. Diamond nanocantilevers are also being developed for ultrasensitive magnetometry8,9 and scanning probe microscopy (SPM).10 In addition, it has been suggested that the chemistry of the diamond surface may be amenable to surface functionalization11 for sensing. To date, the performance of single-crystal diamond nanomechanical resonators has been thoroughly evaluated in vacuum.1,6,7,12 However, vacuum properties will be of little relevance for some applications, such as mass sensing, magnetometry and SPM. Instead, performance in fluids will be consequential especially, when biological or chemical samples are being analyzed in ambient air or in liquids. It is therefore important to elucidate the nanoscale fluid dynamics (or nanofluidics) of diamond nanomechanical resonators. The smooth and inert surface of single-crystal diamond may provide unique opportunities for high-performance operation in fluids. For instance, gases may be accommodated favorably on the diamond surface; the inherent inertness of the diamond surface may allow for reduced drag in water.13 © 2015 American Chemical Society
Received: August 31, 2015 Revised: October 22, 2015 Published: October 28, 2015 8070
DOI: 10.1021/acs.nanolett.5b03503 Nano Lett. 2015, 15, 8070−8076
Letter
Nano Letters
Returning to Figure 1a, we identify several interesting features. Because of angled-etching, the cross sections of the cantilevers are not rectangular but triangular. Figure 1b shows that most of the sidewall surfaces are smooth with an estimated root-mean square (rms) roughness ≲10 nm. The top surface of the cantilever is protected during etches and is much smoother, with an rms roughness
